Fig. 2

The 3D structure of irregular β-trefoil fold proteins used in this study. a 3D structure of Tetanus toxin (PDB ID: 1A8D). b 3D structure of Clostridium neurotoxin type B (PDB ID: 1EPW). c 3D structure of Botulinum neurotoxin serotype A (PDB ID: 3BTA). d 3D structure of CSL bound to DNA (PDB ID: 1TTU). The segment enclosed by a red circle indicates the inserted part. e Schematic drawing of two difference irregular structures